beat-td/Assets/Scripts/HatTower.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class HatTower : MonoBehaviour {

    public Sprite standardSprite;
    public Sprite alternateSprite;

    private AudioSource hatSource;
    private SongData songData;
    private SpriteRenderer spriteRenderer;
    private float cooldown;
    private float cooldownRemaining = 0;

    void Start()
    {
        hatSource = gameObject.GetComponent<AudioSource>();
        songData = GameObject.FindGameObjectWithTag("GameController").GetComponent<SongData>();
        spriteRenderer = gameObject.GetComponent<SpriteRenderer>();
        //The period is 30 / bpm
        cooldown = 11 / songData.bpm;
        //Find next beat
        float nextBeatIn = 30 / songData.bpm - (songData.songTime - (Mathf.Floor(songData.songTime / 30 * songData.bpm) * 30 / songData.bpm));
        InvokeRepeating("OnBeat", nextBeatIn, 30 / songData.bpm);
    }

    void Update () {
        cooldownRemaining -= Time.deltaTime;
        if (cooldownRemaining <= 0)
        {
            cooldownRemaining = 0;
        }
        if (Input.GetKeyDown(KeyCode.Z))
        {
            //Calculate the power of the 
            //power = Sqrt(Cos(pi * t))
            float power = Mathf.Pow(Mathf.Abs(Mathf.Cos(songData.songTime * Mathf.PI * songData.bpm / 30)) * ((cooldown - cooldownRemaining) / cooldown), 2);
            //Play the sound
            hatSource.volume = power;
            hatSource.Play();
            //Start the cooldown
            cooldownRemaining = cooldown;
            //Change the sprite
            spriteRenderer.sprite = alternateSprite;
            Invoke("OnEndAnimation", Time.fixedDeltaTime * 6);
        }
	}

    void OnEndAnimation()
    {
        spriteRenderer.sprite = standardSprite;
    }

    void OnBeat()
    {
        spriteRenderer.color = Color.yellow;
        Invoke("ResetColor", Time.fixedDeltaTime * 2);
    }

    void ResetColor()
    {
        spriteRenderer.color = Color.white;
    }
}